I've used 2,4-D,B on new seedings. We see mostly lambsquarters, but it should do well on pigweeds as well..... as long as you get them when they are small.  Small being like 4" or less.  If they get taller, I don't know how well the 2,4-D,B will control them.  I don't mix it. If you mix 2,4-D,B with grass herbicides like Select, you do have the risk of crop injury due to the additives used with Select. I don't know if that would happen with mixing glyphosate + 2,4-D,B but I do want to raise that possibility.  Maybe it won't be a concern? 

Are your pigweeds ALS resistant? IF not, have you tried Raptor or Pursuit?  Pursuit should be very effective on pigweeds.  However, it is an ALS herbicide-both Raptor and Pursuit are ALS herbicides -  and if your pigweeds are ALS-resistant, that would not work.

edit: if you are applying Velpar in the early spring, I have to wonder if you are applying it too far in advance of when pigweeds are germinating, and it is running out (reducing its half-life) by the time the pigweeds start germinating. Just a thought.....